media: mediatek: vcodec: fix h264 cavlc bitstream fail

Some cavlc bistream will decode fail when the frame size is less than
20 bytes. Need to add pending data at the end of the bitstream.

For the minimum size of mapped memory is 256 bytes(16x16), adding four
bytes data won't lead to access unknown virtual memory.

Fixes: 59fba9ee ("media: mediatek: vcodec: support stateless H.264 decoding for mt8192")
Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_if.c

@@ -539,6 +539,29 @@ static int vdec_h264_slice_core_decode(struct vdec_lat_buf *lat_buf)
 	return 0;
 }
 
+static void vdec_h264_insert_startcode(struct mtk_vcodec_dev *vcodec_dev, unsigned char *buf,
+				       size_t *bs_size, struct mtk_h264_pps_param *pps)
+{
+	struct device *dev = &vcodec_dev->plat_dev->dev;
+
+	/* Need to add pending data at the end of bitstream when bs_sz is small than
+	 * 20 bytes for cavlc bitstream, or lat will decode fail. This pending data is
+	 * useful for mt8192 and mt8195 platform.
+	 *
+	 * cavlc bitstream when entropy_coding_mode_flag is false.
+	 */
+	if (pps->entropy_coding_mode_flag || *bs_size > 20 ||
+	    !(of_device_is_compatible(dev->of_node, "mediatek,mt8192-vcodec-dec") ||
+	    of_device_is_compatible(dev->of_node, "mediatek,mt8195-vcodec-dec")))
+		return;
+
+	buf[*bs_size] = 0;
+	buf[*bs_size + 1] = 0;
+	buf[*bs_size + 2] = 1;
+	buf[*bs_size + 3] = 0xff;
+	(*bs_size) += 4;
+}
+
 static int vdec_h264_slice_lat_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
 				      struct vdec_fb *fb, bool *res_chg)
 {
@@ -582,9 +605,6 @@ static int vdec_h264_slice_lat_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
 	}
 
 	inst->vsi->dec.nal_info = buf[nal_start_idx];
-	inst->vsi->dec.bs_buf_addr = (u64)bs->dma_addr;
-	inst->vsi->dec.bs_buf_size = bs->size;
-
 	lat_buf->src_buf_req = src_buf_info->m2m_buf.vb.vb2_buf.req_obj.req;
 	v4l2_m2m_buf_copy_metadata(&src_buf_info->m2m_buf.vb, &lat_buf->ts_info, true);
 
@@ -592,6 +612,12 @@ static int vdec_h264_slice_lat_decode(void *h_vdec, struct mtk_vcodec_mem *bs,
 	if (err)
 		goto err_free_fb_out;
 
+	vdec_h264_insert_startcode(inst->ctx->dev, buf, &bs->size,
+				   &share_info->h264_slice_params.pps);
+
+	inst->vsi->dec.bs_buf_addr = (uint64_t)bs->dma_addr;
+	inst->vsi->dec.bs_buf_size = bs->size;
+
 	*res_chg = inst->resolution_changed;
 	if (inst->resolution_changed) {
 		mtk_vcodec_debug(inst, "- resolution changed -");